1. Field of the Invention
The present invention relates to rotary pump, and more specifically to high speed piston pumps having variable displacement, such as for use in aircraft fuel and hydraulic systems for pumping, metering and control for aircraft systems including engines.
2. Description of the Related Art
Fixed displacement pumps are conventionally employed as fuel pumps for aircraft turbine engines. Such pumps must be capable of providing sufficient fuel pressure and flow to the engine over a wide range of operating speeds from starting to full throttle operation. Therefore, a common practice is for the pump to produce a relatively high output flow rate at all times. The fuel system meters the pump output flow to supply fuel at a rate that is actually required by the engine. The excess flow from the pump bypasses the engine and is recycled to the pump inlet.
However, circulation in the bypass circuit heats the fuel, which may become excessively hot, especially when a relatively low flow fuel flow rate is demanded by the engine. As a result, a heat exchanger typically is provided in the bypass circuit to cool the fuel before returning it to the pump inlet. This adds complexity, weight and expense to the fuel system.
Size and weight are also important characteristics of components used in aircraft. Thus it is desirable to refine existing piston pump technology to reduce the size, reduce the weight, and increase the operating limits for speed, while providing a high degree of pump reliability.